Known processes for producing elastic polyurethane fibers are dry, wet, and melt spinning systems. In recent years, production of elastic polyurethane fibers by melt spinning has been increasing because this process can give fibers having fine deniers and good transparency at relatively low cost.
However, the elastic polyurethane fibers produced by melt spinning have the essential disadvantages of poorer resistance to heat and hot water than that of elastic polyurethane fibers obtained by dry spinning. There has therefore been demanded improvement in resistance to heat and hot water of elastic polyurethane fibers produced by melt spinning.
The present inventors have proposed a melt-spun elastic polyurethane fiber using a branched polyesterpolycarbonate-based polymer diol and having excellent resistance to heat and hot water (see EP 0449036A2) It has been, however, found that the proposed process can, on laboratory scale, yield elastic polyurethane fibers with good properties but cannot always produce fibers having good properties stably on commercial scales.